<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="f(1)">
<input type="button" value="减" onclick="f(2)">
<input type="button" value="乘" onclick="f(3)">
<input type="button" value="除" onclick="f(4)">
<h3>
    结果:<span></span>
</h3>

<script>
    let i1 = document.querySelector("#i1");
    let i2 = document.querySelector("#i2");
    let s = document.querySelector("span");
    //let inputs = document.querySelectorAll("input");
    // function f1() {
    //     if (isNaN(i1.value) || isNaN(i2.value)) {
    //         s.innerText = "输入错误!";
    //         return;
    //     }
    //     for (let input of inputs){
    //         if (input.value=="加"){
    //             s.innerText = parseFloat(i1.value) + parseFloat(i2.value);
    //         }else if (input.value=="减"){
    //             s.innerText = i1.value - i2.value;
    //         }else if (input.value=="乘"){
    //             s.innerText = i1.value * i2.value;
    //         }else if (input.value=="除"){
    //             s.innerText = i1.value / i2.value;
    //         }
    //     }
    // }
    function f(x) {
        if (isNaN(i1.value) || isNaN(i2.value)) {
            s.innerText = "输入错误!";
            return;
        }
        switch (x){
            case 1:
                s.innerText = parseFloat(i1.value) + parseFloat(i2.value);
                break
            case 2:
                s.innerText = i1.value - i2.value;
                break
            case 3:
                s.innerText = i1.value * i2.value;
                break
            case 4:
                s.innerText = i1.value / i2.value;
        }
    }


</script>
</body>
</html>